Nuclear Theory·nucl-th

Friday·June 10, 2016

5 papers—2 primary·3 cross-listed

03
[Submitted on 9 Jun 2016] (cross-list from astro-ph.HE)
Internal X-ray plateau in short GRBs: Signature of supramassive fast-rotating quark stars?
Ang Li · Bing Zhang · Nai Bo Zhang · He Gao · Bin Qi · Tong Liu
A supramassive, strongly-magnetized millisecond neutron star (NS) has been proposed to be the candidate central engine of at least some short gamma-ray bursts (SGRBs), based on the "internal plateau" commonly observed in the early X-ray afterglow. While a previous analysis shows a qualitative consistency between this suggestion and the Swift SGRB data, the distribution of observed break time $t_{b}$ is much narrower than the distribution of the collapse time of supramassive NSs for the several NS equations-of-state (EoSs) investigated. In this paper, we study four recently-constructed "unified" NS EoSs, as well as three developed strange quark star (QS) EoSs within the new confinement density-dependent mass model. All the EoSs chosen here satisfy the recent observational constraints of the two massive pulsars whose masses are precisely measured. We construct sequences of rigidly rotating NS/QS configurations with increasing spinning frequency $f$ , from non-rotating ( $f = 0$ ) to the Keplerian frequency ( $f = f_{K}$ ), and provide convenient analytical parametrizations of the results. Assuming that the cosmological NS-NS merger systems have the same mass distribution as the Galactic NS-NS systems, we demonstrate that all except the BCPM NS EoS can reproduce the current $22%$ supramassive NS/QS fraction constraint as derived from the SGRB data. We simultaneously simulate the observed quantities (the break time $t_{b}$ , the break time luminosity $L_{b}$ and the total energy in the electromagnetic channel $E_{total}$ ) of SGRBs, and find that while equally well reproducing other observational constraints, QS EoSs predict a much narrower $t_{b}$ distribution than that of the NS EoSs, better matching the data. We therefore suggest that the post-merger product of NS-NS mergers might be fast-rotating supramassive QSs rather than NSs.
Comments:
6 pages, 5 figures, 2 tables, Phys. Rev. D (2016) accepted
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)
arXiv:
1606.02934 [pdf]
PRD(2016)·104 citations
04
[Submitted on 9 Jun 2016] (cross-list from hep-ph)
Modifying the pion mass in the loosely bound Skyrme model
Sven Bjarke Gudnason🇨🇳 · Muneto Nitta🇯🇵
We study the loosely bound Skyrme model with the addition of two different pion mass terms; this is the most general potential of polynomial form up to second order in the trace of the Skyrme field. The two pion mass terms are called the standard pion mass term and the modified pion mass term. We find that the binding energies are not reduced by the introduction of the modified pion mass, but it is analogous to the standard pion mass term with a decrease in the value of the mass parameter of the loosely bound potential (for large values of the latter parameter). We find by increasing the overall pion mass that we can reduce the classical binding energy of the 4-Skyrmion to the 2.7% level and the total binding energy including the contribution from spin/isospin quantization is reduced to the 5.8% level.
Comments:
RevTeX: 28 pages, 13 figures; V2: published version, presentation simplified
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1606.02981 [pdf]
PRD(2016)·26 citations
05
[Submitted on 9 Jun 2016] (cross-list from hep-ph)
Parametrizations of the $γ^{*} N \to Δ (1232)$ quadrupole form factors and Siegert's theorem
G. Ramalho🇧🇷
The large $N_{c}$ limit provides relations that can be used to calculate the $γ^{*} N \to Δ (1232)$ quadrupole form factors at low and intermediate $Q^{2}$ under the assumption of the pion cloud dominance. There are two limitations in those parametrizations. First, the parametrization of the Coulomb quadrupole form factor underestimate the low $Q^{2}$ data. Second, when extrapolated for the timelike region, the form factors violate Siegert's theorem by terms of the order $1/ N_{c}^{2}$ . We propose here corrections to the parametrization of the electric quadrupole form factor, which violate Siegert's theorem only by terms of the order $1/ N_{c}^{4}$ . Combining the improved large $N_{c}$ pion cloud parametrizations with the valence quark contributions based on a covariant quark model for the quadrupole transition form factors, we obtain an extrapolation to the timelike region consistent with Siegert's theorem, and accomplish also a very good description of the data.
Comments:
Published version. Extended version with new title. 6 pages, 4 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1606.03042 [pdf]
PRD(2016)·29 citations

Affiliations

first authorsco-authorsvia INSPIRE

Internal X-ray plateau in short GRBs: Signature of supramassive fast-rotating quark stars?

Modifying the pion mass in the loosely bound Skyrme model

Parametrizations of the γ∗N→Δ(1232) quadrupole form factors and Siegert's theorem

Affiliations

Parametrizations of the $γ^{*} N \to Δ (1232)$ quadrupole form factors and Siegert's theorem